September 26, 2018
Waders such as red knots Calidris canutus gather in large non-breeding flocks in the Wadden Sea, where they forage on the intertidal mudflats
Wadden Sea mudflats
Knots can use social information in lab settings to find food[1], and may learn the location of profitable foraging patches by observing flock-mates[2]
1: Bijleveld et al. 2015. Behav. Processes 2: Bijleveld et al. 2010. Oikos
Knots benefit from association, but do they have friends — persistent, non-random associations — within & between tidal intervals[3][4]?
3: Myers 1983. Behav. Ecol. Sociobiol. 4: Conklin & Colwell 2007. J. Field. Ornith.
We set up ATLAS — a tracking tower system (n = 5) based on the Time of Arrival (ToA) of radio signals from tagged knots (n = 35)
Tracking tower and locations
We obtained water-level data from Harlingen
Identified 44 tidal intervals (~12 hrs) over 19 calendar days
Grouped each knot's movement tracks by tidal interval
Calculated co-occurrence cij
cij = proportion of positions at which birds i & j were within 250 m of each other
Pair-wise co-occurrence distribution
Pair-wise co-occurrence matrix
% of pairs with cij values higher than expected
GLMM: post-foraging cij ~ pre-foraging cij + foraging period distance mismatch + (1|pair) + (1|tidal interval)
Pre-foraging cij is not a significant effect (z = 1.738, p-value = 0.08)
Knots don't re-unite with pre-foraging 'friends'
Wader interactions may occur at scales not measured here
Knots have previously been shown to be non-randomly associated[5]
5: Harrington & Leddy 1982. Wader Study Group Bull.
Knots have consistent personalities re: exploratory behaviour[6]
May associate with individuals of similar personality due to shared resource requirements
Identification of neighbour personality may still require sustained association
6: Bijleveld et al. 2014. Proc. Royal Soc. B
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